The invention relates to a radiation-sensitive semiconductor device comprising a semiconductor body including a substrate carrying a semiconductor layer, which is thin relative to the substrate and which comprises a radiation-sensitive semiconductor material, in which semiconductor layer a semiconductor element having electrical connections is formed which is sensitive to electromagnetic radiation incident on the surface of the semiconductor body, and radiation-reflecting means being provided between the substrate and the semiconductor layer. The invention also relates to a method of manufacturing such a device.
Such a device can very suitably be used as a detector in various optical systems, such as an optical glass fiber communication system or an optical disc system. By virtue of the small thickness of the semiconductor layer and the presence of the reflection means, the radiation-sensitive element can be of the so-called resonant-cavity type, that is the radiation to be detected traverses the radiation-sensitive layer a number of times. As a result, also radiation which is only very little absorbed by the radiation-sensitive semiconductor material can be satisfactorily detected. By virtue of the small thickness of the semiconductor layer, the semiconductor element formed therein still has a high response rate. The response of such a device exhibits a periodical variation in the wavelength domain. This enables the response to be accurately attuned to the wavelength of the radiation to be detected. If this wavelength is situated in or near the visible part of the spectrum, the device is hardly sensitive to (visible) background radiation. Consequently, the device can be regarded as a monolithic integration of a detector and a filter.
Such a device and method are known from U.S. Pat. No. 5,525,828, published on Jun. 11, 1996. Said known device comprises (see for example FIG. 20) a photodiode which is formed in a relatively thin semiconductor layer of silicon which is situated on a silicon substrate and separated therefrom by a first electrically insulating layer of silicon dioxide which serves as a mirror for the radiation incident on the semiconductor layer. At the upper side of the thin semiconductor layer, i.e. where the radiation to be detected is incident, there is also an electrically insulating layer, which is also made of silicon dioxide and which also serves as a (partly pervious) mirror. Said known device comprises two semiconductor regions which are recessed in the surface and situated at some distance from each other, said semiconductor regions being, respectively, of the n-conductivity type and the p-conductivity type and provided with electrical connections.
A drawback of the known device is that the wavelength selectivity thereof is insufficient for certain applications. Besides, it is also difficult to attune the properties of the device to a desired wavelength.